Specific gravity indicator or recorder



Dec. 29,1931. HOD SON 1,838,399

SPECIFIC GRAVITY INDICATOR OR RECORDER Filed Jan. 28, 1951 4Sheets-Sheet 1 5 I I I a v I a i 1 Dec.29, 1931. 4 My HD SON 1,838,399

SPECIFIC GRAVITY INDICATOR OR RECORDER Filed Jan. 28, 1951 4Sheets-Sheet 2 Dec. 29, 1931.

J. L. HODGSON SPECIFIC GRAVITY INDICATOR OR RECORDER Filed Jan. 28, 19314 Sheets-Sheet 3 Hill Dec. 29, 1931. J. HODGSON 1,838,399

SPECIFIC GRAVITY INDICATOR 0R RECORDER Filed Jan. 28, 1931 4Sheets-Sheet 4 lllllll HIHIIIH Patented Dec. 29, 1931 UNITED ST TESPATEIAN OFFICE-Q1 1 .Ion v LAWRENCE HonGsoN; .oRLUTon, EnG-LANn'AssIGNoRr GEORGE, KENT,

" minimal or Lennon ENGLAND srncrrio GRAVITY InmoAT'oitoR REcoRnERilpplication ma ianuar 28, 1931, Serial No. 511,827,".and in GreatBritain. December 1929.

i The present inventionbrelates to devices suitable for indicating or;recordmg variations in the specific gravity of a fluid passmg in apipe.

. 5 ,The invention is illustrated-in.the accompanying drawings in whichFigural is a vertical sectional elevation, Figure'2 a plan view partlyin section with the top cover plate removed, Figure 3 an end sectionalelevation and Figure 4 a front elevation. iFigure 5 is a diagrammaticviewf of a modification, and Figures G and 6*, to be jointlyconsidered,are left hand and right hand portions, respectively, of a sectionalelevation of a further modification. .e c Referring more particularly toFigures 1-4,.1, 2 are displacers of widely different weights per unitvolume, but of approximatelyequalweights, the displacer 1 being that dof smaller weightper nnit volume and being made hollow The displacersare secured to two opposite arms 3,,& forming a beam which is :pivotallymounted about aknifeedge 5v and whose positionis controlled by apendulumweight 6. An adj usting weight 7 is provided which is soadjusted thattwhenthe displacers areimmers ed in:liquid of the meanspecific gravity to. be indicated or recorded,

' there will be no deflection from the mean position, i. e. thependulum. weight will hang vertically. If the liquid in which thedisplacers are immersed is now,replaced by a liquidoflower specificgravity, the arm-carrying the displacer 1 will descend, owingto as itsgreater loss of buoyancy, The amount that it willdescend will dependupon the size and the positionof the controlling'pen'dulum weight, sothat a definite deflection will be obtainedfor each specific gravity ofthe liquid in which the beam carryingthe two displacers and thecontrolling weight isimmerse'd.

As "an apparatus constructe'd' aas above would show a deflection due toa fall in the specific gravity'of the liquid in which the displacerswere immersed due to any rise-in tem- 9 is arrangedon the periphery ofthe circular perature, of that liquid, the following means are providedto render theindications of the 'apparatusunalfected by such changes oftemperature. i i

Thehollfow displacer 1 is filled with liquid 6 of the-same coefficient,of-expansion as the liquid whosespecific gravity it is desired toindicate or record. The arm 3 carrying this dis'placer is als0madehollow,and communir cates with a closed cylindrical chamber 8 wliosecentre is at the centre'of' rotation of the knife edge- 5 which carriesthe beam with its two dis'p-lacersand pendulum control weight; Thetubular arm carryingthe large 'displacer liis bent downwards into thisclosed cylindrical cavity which is partially filled with liquid so thatthe end of this tubular arm is always sealed by the liquid, the beambeing adjusted for balance by means of the adjusting weights. A suitablefilling plug chamber, so-Y long as the coeflicients of vexpansion oftheliquids inside and outside the displacer are substantially equal,changes in the common temperatureof these liquids/will not appreciablyaffect the balancerof the beam as, an amountof liquid Whose weight isequal to, the lossof buoyancy, of the displacer 1 will expand into thecentralcylindrical chamber 8 where itproduces no mo- *7 V -ment'aboutthe knife edge since the pivot means 5 are at the volumetric orsymmetrical j center of the vessel 8. The apparatus is thereforecompensated for changes the specific gravity of the liquid inwhich thfedisplacers are immersed, due to variations from thefmean temperature atwhich the zero of the beam was adjusted" bymeans of the adjustingweights. I 'f If theadjustingand controlling weights are made ofdifferent materials their expansions must be suitably compensated.

The error due totheiloss of buoyancy with fall of specific gravity withrise. of temperature'of the'liquid in which the controlling pendulumweight is immersed is a small fraction of 1 per cent over any reasonablerange of temperature, and therefore it does not generally requirecompensation. A compensation can, however, be efiected by fitting abovethe pivotal axis of the arm 3 a volume the moment of whose buoyancy isequal to that of the controlling pendulum weight, but whose weight ismuch less.

The apparatus above described is located within a chamber in a casing 10havinginlet and outlet connections 11, 12 for theliquid whose specificgravity is to be measured. Secured to the casing is a second casing 13containing a chart 14 over which moves a pen 15. The pen is operated bythe movement of the beam through a bracket 16 which is secured to thebeam and to an extension 17 i of a frame 18 carrying the pen and havinga knife edge pivot 19.

Battles 20, 21 are arranged in the chamber to enable the liquid thereinto be continually exchanged without causing any deflection of thebalance arm.

In the modification shown in Figure 5, the displacer 1, hollow arm 3 andcentral chamher 8' are completely filled with liquid, and in order toallow the temperature compensation to be obtained, the central chamberis extensible to accommodate an increase in volume of the liquid, due totemperature rise. To efiect this, one (or both) of the ends of thechamber is closed by concentric flexible tubes 22, 23 and an annularplate 24. Such an arrangement of temperature compensation isparticularly suitable for use where the fluid whose specific gravity isbeing measured is under high pressure.

If the liquid is under pressure, the balance arm carrying the displacersmust also be under pressure, and the motion of the arm is most suitablytransmitted outside the pressure tight casing by means of a magneticdrive. Such an arrangement is illustrated in Figure 6 and consists oftwo magnets 25, 26 operating through a window of nonmagnetic material,the magnet 25 being attached to the beam and the magnet 26 to the frame18 carry the pen.

In this arrangement also the temperature compensation may bealternatively effected by forming the end walls of the displacer 1 bycorrugated flexible plates 27 which allow the liquid freely to expandand contract on varia tion in temperature.

What I claim is 1. In apparatus for measuring the specific gravity of afluid, the combination of a hol low displacer of 'fixed capacity whichis adapted to move in response to variations in the specific gravity ofthe fluid to be measured, and is adapted to contain fluid, a sealedvessel, and means connectingsaid displacer and vessel and permittingfluid to pass between the displacer and the sealed vessel to compensatefor variations in the specific gravity, due to variations in thetemperature of the fluid to be measured, said vessel, displacer andmeans constituting a unit, and means fulcruming the unit on an axispassing through said vessel.

2. In apparatus for measuring the specific gravity of a fluid, thecombination of a hollow displacer of fixed capacity which is adapted tocontain fluid, a sealed vessel, and means connecting said displacer andvessel and permitting fluid to pass between the displacer and the sealedvessel to compensate for variations in the specific gravity, due tovariations in the temperature of the fluid to be measured said vessel,displacer and means constituting a unit fulcrumed on an axis passingthrough the volumetric center of said vessel whereby the latter islocated so that the movement of the displacer about said axis isunaffected by the contents of the vessel.

3. In apparatus for measuring the specific gravity of a fluid, thecombination of a rocking beam, a pair of displacers supported on therocking beam, one of the displacers being hollow, of fixed capacity, andadapted to contain fluid, a sealed vessel, and means permit ting fluidto pass between the hollow displacer and the sealed vessel to compensatefor variations in the specific gravity, due to temperature variations ofthe fluid to be meas ured, said vessel, displacers, rocking beam andmeans constituting a unit fulcrumed on an axis passing through thevolumetric center of the vessel whereby the latter is located so thatthe movement of the displacer about said axis is unaffected by thecontents of the vessel.

4:. In apparatus for measuring the specific gravity of a fluid, arocking arm, a hollow displacer supported by the arm and which is offixed capacity and is adapted to move in response to variations in'thespecific gravity of the fluid to be measured, a sealed flexible vessel,means placing the vessel in communication with the interior of thedisplacer and symmetrically disposed about a vertical plane passingthrough the pivotal axis of the arm, the displacer and flexible vesselbeing adapted to be filled with fluid and the flexible vessel permittingfluid to pass out of and into the displacer to compensate for variationsin the specific gravity, due to variations in temperature of the fluidto be measured.

5. In apparatus for measuring the specific gravity of a liquid, arocking arm, a hollow displacer carried by the rocking arm and of fixedcapacity, the displacer being adapted to be filled with liquid andadapted to move in response to variations in the specific gravity oftheliquidto be measured, and a sealed vessel means placing the vessel incommunication with the interior of the displacer and partially filledwith liquid so that the point of communication with the displacer isconstantly under liquid seal, the vessel being so arranged that itscontents are symmetrical about a vertical plane'passing t roughthepivotal axis of the arm so that liquid can pass between thedisplacerand vessel'to compensate for variations in the specific gravity, due tovariations in temperature of the liquid to be measured. 1

' In testimony that I claim the foregoing as my invention I have signedmy name this 14th day of January, 1931.

JOHN LAWRENCE HODGSO-N.

